Condensation copolymers having supressed crystallinity

ABSTRACT

Condensation copolymers are disclosed which are polymerized from a first monomer which is capable of polymerization by condensation polymerization, e.g., ring opening lactone polymerization, and a second monomer which is effective to suppress the crystallization of the copolymer. It is disclosed that suppression of the crystallization can provide enhanced mechanical properties in films made from the copolymers. As a result, films prepared from the copolymers of the present invention can have properties rendering them suitable for use as biodegradable trash bags as well as for other uses.

FIELD OF THE INVENTION

The present invention relates to condensation copolymers, e.g.,polyesters, having suppressed crystallinity which can render themsuitable for use, for example, in the manufacture of biodegradable filmsfor trash bags.

BACKGROUND OF THE INVENTION

Current environmental concerns have generated interest in the use ofbiodegradable plastics for disposable items such as, for example, trashbags, packaging materials, eating utensils, and the like. A variety ofbiodegradable polymers have been proposed for such uses. Typical of suchpolymers include, condensation polymers, such as, for example,polyesters, polyester amides, polymers formed by ring openpolymerization, e.g., lactone, lactide and lactam polymerizations,polyhydroxyalkonoates, polylactic acid and naturally occurring polymers,such as, polysaccharides, e.g., cellulosic, starch, and soy derivatives.

As used herein, the term “biodegradable”, as defined in ASTM D-883, ismade with reference to degradable polymers in which the degradationresults from the action of micro-organisms occurring naturally such as,for example, bacteria, fungi, and algae. The biodegradability may beevidenced, for example, by the production of CO₂ and associatedreduction in mechanical properties, such as tensile strength and percentelongation at break. Further details are known to those skilled in theart.

Although many polymers such as those described above, are highlyeffective in terms of their biodegradability, they often suffer frominferior mechanical performance which has hindered their commercialviability. More specifically, when converted to film by blown filmextrusion, for example, biodegradable polymers often do not have goodmachine direction (“MD”) Elmendorf Tear Strength as measured by ASTMD-1922, transverse direction (“TD”) Tensile Impact as measured by ASTMD-1822, Falling Dart Impact Resistance as measured by ASTM D-1709, MDand TD Secant Modulus as measured by ASTM D-882, and Puncture Resistanceas measured by Union Carbide Test Method WC-68-L. On the other hand,when biodegradable polymers are modified to enhance their mechanicalproperties, their biodegradability often suffers.

As used herein, the terms “condensation polymerization” and“polycondensation” mean: (i) a polymerization reaction in which two ormore molecules are combined with the generation of water, alcohol orother simple substances as by-products; and (ii) polymerization ofmonomers, e.g., ester and amide monomers, formed by ring openingpolymerization, e.g., lactones, lactides and lactams, which do notgenerate water, alcohol or other simple substances as by-products.

Often, condensation polymers suitable for use as biodegradable materialsare semi-crystalline in form, e.g., greater than about 30%, oftengreater than about 50% and more often greater than about 70%crystalline. Complete crystallization of polymers is often a slowprocess requiring minutes, hours or days to fully accomplish. Whencrystallization is desired, the temperature is held above the glasstransition temperature (“Tg”) and below the crystalline melting pointfor a time sufficient to allow the molecules of the polymer to orderthemselves into crystal lattices. This process is also referred to inthe art as “annealing”. If the crystallinity of the polymer becomes toohigh, the molded article from the polymer may not have sufficienttoughness to be viable in a typical end use like trash bags, mulch film,molded parts and the like.

Accordingly, improved condensation polymers having enhanced mechanicalproperties are desired which can retain their biodegradablecharacteristics.

SUMMARY OF THE INVENTION

By the present invention, improved condensation polymers are provided.The improvement of the present invention is directed to the use ofcomonomers in the condensation polymerization which are effective tosuppress the crystallinity of the copolymers. Without being bound to anyparticular theory, it is believed that the suppression of crystallinitycan cause enhancements in the mechanical properties of films made fromthe copolymers compared to copolymers made without thecrystallinity-suppressing monomers.

In accordance with the present invention, the suppression ofcrystallinity may be evidenced by one or more factors. For instance, thesuppression of crystallinity may be evidenced by a reduction in thecrystallization temperature of the copolymer, or by a reduction in therate of crystallization of the copolymer, or by a reduction in the melttemperature of the polymer or by a reduction in the crystallinity of thecopolymer. As used herein, the term “crystallization temperature” meansthe temperature at which formation of the crystalline phase occurs; theterm “crystallization rate” means the rate at which formation of thecrystalline phase occurs; the term “melt temperature” means the freezingpoint and the term “crystallinity” means the degree of crystallinity ofthe polymer. The crystallization properties of polymers can be readilydetermined by those skilled in the art, such as, for example, bydifferential scanning calorimetry (“DSC”).

DETAILED DESCRIPTION OF THE INVENTION

The first monomer suitable for use in accordance with the presentinvention can be any monomer which is polymerizable by condensationpolymerization. The first monomer can be ethylenically unsaturated oralternatively can have no ethylenic unsaturation. The molecularstructure of the first monomer is not critical for the present inventionand can be straight, e.g., normal, alkyl or branched, cyclic oraromatic. Preferably, the first monomer has functional groups selectedfrom the group consisting of esters, ethers, alcohols, acids, amines,amides, acid halides, isocyanates and mixtures thereof as may bedetermined by those skilled in the art. In addition, the first monomercan be comprised of a single molecular unit, an oligomer or a prepolymerand can have a molecular weight of typically from about 62 to 12,000grams per gram mole (“g/gmol”), more typically, from about 62 to 10,000g/gmol.

Unless otherwise indicated, as used herein, the term “molecular weight”means number average molecular weight. Techniques for determining numberaverage molecular weight are known to those skilled in the art. One suchtechnique is gel permeation chromatography (“GPC”).

In one aspect of the present invention, the first monomer comprises oneor more compounds which can be polymerized or copolymerized to formaliphatic polyesters or polyester amides or other condensation polymers.Examples of such polymers include, for example, polyesters prepared fromthe reaction of C₂-C₆ diols, e.g., ethylene glycol, diethylene glycol,butanediol, neopentyl glycol, hexanediol with dicarboxylic acids, suchas but not limited to, succinic, glutaric or adipic acid; copolyestersof terephthalic acid based polymers with dicarboxylic acids and diols;and polyester/amides from the reaction of caprolactam with dicarboxylicacids and diols. Suitable hydroxy acids include, for example,α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid,α-hydroxyisovaleric acid, α-hydroxycaproic acid, α-hydroxyisocaproicacid, α-hydroxy-α-ethylbutyric acid, α-hydroxy-β-methylvaleric acid,α-hydroxyheptanoic acid, α-hydroxyoctanoic acid, α-hydroxydecanoic acid,α-hydroxymyristic acid and α-hydroxystearic acid or their intermolecularcyclic esters or combinations thereof.

In another aspect of the present invention, the first monomer comprisescyclic monomers which are polymerized by ring opening polymerization.Typical of such monomers are cyclic esters, such as, for example,lactides, glycolides, lactones and cyclic carbonates.

In one aspect of the present invention, the cyclic monomers includethose having the formulas:

where X=nil, —O—, or —O—C=O; Z=1-3; Y=1-4; R₁-R₄=H—, —CH₃, C₂-C₁₆ alkylgroup, —C(CH₃), or HOCH₂—, and where all R's are independent on each yor z carbon unit and independent of each other; or

where R₁-R₄=H—, —CH₃, C₂-C₁₆ alkyl group, or HOCH₂—, and where all R'sare independent of each other.

Examples of the lactones described above are, but not limited to,ε-caprolactone, t-butyl caprolactone, zeta-enantholactone,deltavalerolactones, the monoalkyl-delta-valerolactones, e.g. themonomethyl-, monoethyl-, monohexyl-deltavalerolactones, and the like;the nonalkyl, dialkyl, and trialkyl-epsilon-caprolactones, e.g. themonomethyl-, monoethyl-, monohexyl-, dimethyl-, di-n-propyl-,di-n-hexyl-, trimethyl-, triethyl-, tri-n-epsilon-caprolactones,5-nonyl-oxepan-2-one, 4,4,6- or 4,6,6-trimethyl-oxepan-2-one,5-hydroxymethyl-oxepan-2-one, and the like; beta-lactones, e.g.,beta-propiolactone, beta-butyrolactone gamma-lactones, e.g.,gammabutyrolactone or pivalolactone, dilactones, e.g. lactide,dilactides, glycolides, e.g., tetramethyl glycolides, and the like,ketodioxanones, e.g. 1,4-dioxan-2-one, 1,5-dioxepan-2-one, and the like.The lactones can consist of the optically pure isomers or two or moreoptically different isomers or can consist of mixtures of isomers.

In addition cyclic carbonates of the formula:

where X=nil,—O—; Z=1-3; Y=1-3; R₁-R₄=H—, —CH₃, C₂-C₁₆ alkyl group, orHOCH₂—, and where all R's are independent on each y or z carbon unit andindependent of each other, can be used as a comonomer with the lactonesof this invention.

Examples of suitable cyclic carbonates are ethylene carbonate,3-ethyl-3-hydroxymethyl trimethylene carbonate, propylene carbonate,trimethylene carbonate, trimethylolpropane monocarbonate,4,6-dimethyl-1,3-propylene carbonate, 2,2-dimethyl trimethylenecarbonate, and 1,3-dioxepan-2-one.

ε-caprolactone and its derivatives and other seven membered ringlactones are especially preferred for use as first monomers inaccordance with the present invention.

Examples of typical cyclic ester polymers and their (co)polymersresulting from the polymerization of the above-mentioned monomersinclude: poly(L-lactide); poly(D,L-lactide); poly(mesolactide);poly(glycolide); poly(trimethylenecarbonate);poly(epsilon-caprolactone); poly(L-lactide-co-D,L-lactide);poly(L-lactide-co-meso-lactide); poly(L-lactide-co-glycolide);poly(L-lactide-co-trimethylenecarbonate);poly(L-lactide-co-epsilon-caprolactone);poly(D,L-lactide-co-meso-lactide); poly(D,L-lactide-co-glycolide);poly(D,L-lactide-co-trimethylenecarbonate);poly(D,L-lactide-co-epsilon-caprolactone);poly(meso-lactide-co-glycolide);poly(meso-lactide-co-trimethylenecarbonate);poly(meso-lactide-co-epsilon-caprolactone);poly(glycolide-co-trimethylenecarbonate);poly(glycolide-co-epsilon-caprolactone).

Typically, the amount of the first monomer used in the copolymers of thepresent invention is from about 50 to 99 wt. %, preferably from about 60to 98 wt. % and more preferably from about 85 to 95 wt. %, based on thetotal weight of the monomers in the copolymer. Monomers suitable for useas the first monomer in the copolymers of the present invention arecommercially available.

The second monomer suitable for use in preparing the copolymers of thepresent invention includes any monomers which are functional to suppressthe crystallinity of the copolymer. Preferably, the second monomer isamorphous. As used herein, the term “amorphous” means that the monomeris predominately amorphous, i.e., greater than 50% amorphous, preferablygreater than 70% amorphous and more preferably greater than 90%amorphous, as determined, for example, by DSC measuring the enthalpy offusion.

The second monomer can be ethylenically unsaturated or alternatively canhave no ethylenic unsaturation. The molecular structure of the secondmonomer is not critical for the present invention and can be straight,e.g., normal, alkyl or branched, cyclic or aromatic. In a preferredaspect of the invention, the second monomer is a branched ester.Preferably, the second monomer has a functional group selected from thegroup consisting of esters, ethers, alcohols, acids, amides, acidhalides and mixtures thereof. In addition, the second monomer can becomprised of a single molecular unit, an oligomer or a prepolymer andcan have a molecular weight of typically from about 62 to 12,000 g/gmol,more typically, from about 62 to 10,000 g/gmol. Additionally, the secondmonomer can comprise a derivative of the first monomer, e.g, a branchedcaprolactone such as, for example, t-butyl caprolactone.

Often, the second monomer is used as an initiator in the polymerizationof the first monomer, e.g., to initiate ring opening of cyclic lactonemonomers. Typically, the suppression in crystallinity afforded by thesecond monomer will be evidenced by one or more of the followingfactors: (i) a reduction in the crystallization temperature of thecopolymer of at least 2° C., preferably at least 4° C. and morepreferably at least 6° C., as compared to a homopolymer of the firstmonomer or a copolymer of the first monomer and another monomer which isnot effective to suppress the crystallinity, or (ii) a reduction in thecrystallinity of the copolymer. Typically, in accordance with thepresent invention, the crystallinity will be reduced by at least 2percent, preferably at least 6 percent and more preferably at least 8percent compared to the crystallinity of a homopolymer of the firstmonomer or a copolymer of the first monomer and another monomer which isnot effective to suppress the crystallinity. The crystallinity can bedetermined by DSC, measuring the enthalpy of fusion.

In one aspect of the present invention, the second monomer is effectiveto create amorphous regions in the copolymer. For example if the secondmonomer is a branched version of the first monomer, it generally willnot co-crystallize with the first monomer, thus it will disrupt thecrystallization of the first monomer, increasing the amorphous region,decreasing the crystallinity of the copolymer. If the second ‘monomer’is a non-crystallizable oligomer, the net crystallinity of the copolymerwill be reduced to a level that can enhance molded polymer toughness.

In another aspect of the present invention, the second monomer iseffective to introduce branching into the polymer, i.e., pendant chainsoff the backbone of the copolymer. Preferably, the branching isintroduced as short chains into the copolymer backbone. As used herein,the term “short chain branching” means hydrocarbon branches, e.g., alkylgroups in the polymer backbone, which are preferably, C₁ to C₁₆ alkylgroups, which terminate in an unreacted free end, e.g., methyl, propyl,t-butyl. Short chain branching can be introduced into the polymerbackbone, for example, by using branched difunctional initiatorsobtained by polymerizing a linear or branched dicarboxylic acid with alinear or branched diol initiator, such that at least either the acid ordiol is branched.

Suitable dicarboxylic acids are of the formula:

where Y=0 to 12; R₁ and R₂ =H—, —CH₃ or C₂-C₁₆ alkyl group, and whereall R's are independent of each other and each carbon unit.

Illustrative of the dicarboxylic acids are succinic acid, glutaric acid,adipic acid, suberic acid, sebacic acid, dodecanedioic acid, and2-ethyl-2-methylsuccinic acid. In addition to the aliphatic dicarboxylicacids described above, aromatic dicarboxylic acids, such as but notlimited to phthalic acid, isophthalic acid, and terephthalic acid can beused.

Suitable diol initiators are of the formula:

where X=nil, —O—; a=1 to 6; b=0 to 10; c=nil, C₁-₆; and R₁-R₄=H—, —CH₃or C₂-C₁-C₁₆ alkyl group, and where all R's are independent of eachother and each carbon unit. Examples of diols are, but not limited to,ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol,1,6-hexanediol, 1,10-decanediol, 1,12-dodecanediol, 1,2-decanediol,1,2-dodecanediol, 1,2-hexadecanediol, neopentyl glycol,3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol,2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-3-butyl- 1,3-propanediol,2-ethyl- 1,6-hexanediol.

Of these, 2-butyl-2-ethyl-1,3-propane adipate, prepared from thereaction of 2-butyl-2-ethyl-1,3-propanediol.(“BEPD”) and adipic acid arepreferred. Other methods of introducing short chain branching includethe reaction of either the branched or long chain 1,2-diol withε-caprolactone monomer and then tranesterification with the diester of adicarboxylic acid, e.g., transesterification of a BEPD initiatedcaprolactone oligomer with dimethyladipate, or the reaction of a BEPDinitiated caprolactone oligomer with adipoyl chloride, or the reactionof a BEPD initiated caprolactone oligomer with a diisocyanate, i.e. HDIor MDI, or reacting branched lactones with unbranched lactones, e.g.copolymer of t-butyl caprolactone and E-caprolactone. As an alternativeor in addition to the polymerized branched monomers, branched polymerscan be blended into linear polymers of other molecules to provide shortchain branching.

The amount of the second monomer suitable for use in preparing thecopolymers of the present invention is effective to suppress thecrystallinity of the copolymer. Typically, the amount is from about 1 to50 wt. %, preferably from about 5 to 35 wt. % and more preferably fromabout 9 to 20 wt. % based on the total weight of the monomers used tomake the copolymer. The optimal level of the second monomer will dependof the specific structure of the second monomer and can be determined bythose skilled in the art.

One or more monomers from each of the first monomer group or secondmonomer group may be used in preparing the copolymers of the presentinvention. In addition, other monomers may also be employed in additionto the first monomer and second monomer. Such other monomers may beintroduced for example in order to impart certain desired properties tothe copolymer. The particular other monomers are not critical to thepresent invention but may include for example, monomers such asdialcohols, e.g., ethylene glycol, 1-4-butanediol, 1,3-propanediol, 1,6hexanediol, diethylene glycol, etc., dicarboxylic acids, e.g., oxalicacid, succinic acid, adipic acid, amino alcohols, e.g., ethanol amine,propanol amine, amino carboxylic acids, e.g., amino caproic acid and thelike. In addition, other monomers can be employed which are normallyused to make traditionally non-biodegradable polymers, such as, forexample, polyethylene (including low density polyethylene, linear lowdensity polyethylene and high density polyethylene), ethylene vinylacetate copolymers, ethylene acrylic acid copolymers, polyvinylchlorides, polystyrenes, chlorinated polyethylenes, ethylene propylenecopolymers, acrylic acid copolymers, polyvinyl acetals copolymers,polyamines, polyethylene terephthalates, phenolic resins and urethanes.

In addition to other monomers, the copolymers of the present inventionmay be blended and/or reacted with other polymers to provide desiredcharacteristics. For instance, the copolymers of the present inventionmay be extruded with other polymers, such as, for example,polysaccharides, e.g., starch, cellulosics, chitans and the like.Further details of such blended polymer compositions are known to thoseskilled in art. See for example, U.S. Pat. No. 5,095,054 which isdirected to thermoplastic polymer compositions comprising destructurizedstarch and other polymers, U.S. Pat. No. 5,540,929 which is directed toaliphatic polyester grafted polysaccharides.

Typically, the amount of such other monomers when used in the copolymersof the present invention is from about 1 to 90 wt. %.

Typically, when the copolymers of the present invention are blended orreacted with other polymers, the amount of the other polymer istypically from about 0 to 70 wt. % and preferably from about 20 to 60wt. % and more preferably from about 30 to 40 wt. % based on the totalweight of the blended polymer composition.

Another aspect of the present invention is directed to the introductionof long chain branching into the polymer backbone. In this aspect of theinvention, long chain branching can be incorporated in the polymerbackbone or polymers containing long chain branching can be blended withthe copolymers to improve the processability. As used herein, the term“long chain branching” means hydrocarbon branches, e.g., alkyl groups inthe backbone which terminate in more than two reactive end groups whichresult in the preparation of nonlinear polymers. Examples of polymerswith long chain branching are, but not limited to, polymers ofE-caprolactone with multifunctional initiators such astrimethylolpropane, pentaerythritol, dipentaerythritol and othermolecules with multiple hydroxyl or other reactive groups.

The improved processability of the copolymers of the present inventioncan be measured, for example, by determining their Relaxation SpectrumIndex (RSI) values. As used herein, the terms “Relaxation SpectrumIndex” and “RSI” mean the breadth of the distribution of melt statemolecular relaxations as calculated from dynamic oscillatory shear testsrun in a frequency range from 0.1 to 100 1/ sec. The RSI is a sensitiveindicator of molecular structure, such as long chain branching, thatleads to long relaxation time behavior in the melt state. Furtherdetails concerning RSI are known to those skilled in the art. See, forexample, J. M. Dealy and K. F. Wissbrun, Melt Rheology and Its Role inPlastics Processing, Van Nostrand Reinhold, 1990, pp. 269-297 and S. H.Wasserman, J. Rheology, Vol. 39, pp. 601-625 (1995).

The processes used to prepare the copolymers of the present inventionare not critical. The polymer of the present invention can be preparedby bulk polymerization, suspension polymerization, extruder or solutionpolymerization. The polymerization can be carried out, for example, inthe presence of an inert normally-liquid organic vehicle such as, forexample, aromatic hydrocarbons, e.g., benzene, toluene, xylene,ethylbenzene and the like; oxygenated organic compounds such as anisole,dimethyl, and diethyl esters of ethylene glycol; normally-liquidhydrocarbons including open chain, cyclic and alkyl-substituted cyclicsaturated hydrocarbons such as hexane, heptane, cyclohexane,decahydronapthalene and the like.

The polymerization process can be conducted in a batch, semi-continuous,or continuous manner. The monomers and catalysts can be admixed in anyorder according to known polymerization techniques. Thus, the catalystcan be added to one comonomeric reactant. Thereafter, thecatalyst-containing comonomer can be admixed with another comonomer. Inthe alternative, comonomeric reactants can be admixed with each other.The catalyst can then be added to the reactant mixture. If desired, thecatalyst can be dissolved or suspended in an inert normally-liquidorganic vehicle. If desired, the monomeric reactants either as asolution or a suspension in an inert organic vehicle can be added to thecatalyst, catalyst solution or catalyst suspension. Still further, thecatalyst and comonomeric reactants can be added to a reaction vesselsimultaneously. The reaction vessel can be equipped with a conventionalheat exchanger and/or mixing device. The reaction vessel can be anyequipment normally employed in the art of making polymers. One suitablevessel, for example, is a stainless steel vessel. A plasticizer, ifused, or a solvent can be blended into the polymer to aid in removal ofthe polymer material from the reactor vessel.

Typically, the polymerization reactions are conducted at a temperatureof from about 70 to 250° C., preferably from about 100 to 220° C., overa reaction time of from about 3 minutes to 24 hours preferably fromabout 5 to 10 hours. The reaction pressure is not critical to thepresent invention. The particular catalyst used in the polymerization isnot critical and can be determined by those skilled in the art. However,one preferred catalyst for the polymerization of caprolactone with BEPDadipate is tin carboxylate. The catalyst and initiator may be combinedin the same molecule, e.g., a aluminum alkoxide.

In addition to the monomers, other ingredients may be added, such asplasticzers, e.g. epoxidized soybean oil, epoxidized linseed oil,triethyl citrate, acetyltriethyl citrate, tri-n-butyl citrate,acetyltri-n-butyl citrate, acetyltri-n-hexyl citrate, glycerin,diethylphthalate, dioctylphthalate; slip/antiblocks, e.g. stearamide,behenamide, oleoamide, erucamide, stearyl erucamide, erucyl erucamide,oleyl palmitamide, steryl stearamide, erucyl stearamide, N,N′-ethylenebisstearamide, N,N′-ethylenebisoleamide, talc, calciumcarbonate, kaolin clays, molecular sieves and other particulatematerials, stabilizers, compatabilizers, nucleating agents, pigments,etc. Typically, the total amount of such other ingredients ranges fromabout 0.01 to 10 weight percent, based on the total weight of thecopolymer composition. Further details concerning the selection andamount of such additives are known to those skilled in the art.

The copolymers produced in accordance with the present inventiontypically have a melting point of from about 50 to 240° C., preferablyfrom about 52 to 120° C., and a Tg of from about −120 to 120° C. andpreferably from about −60 to 60° C. The copolymers typically have a MeltFlow of from about 0.1 to 7, preferably from about 0.2 to 2.5 and morepreferably from about 0.5 to 2. As used herein, the term “Melt Flow”means grams of material that flow through a die in ten minutes at 125°C./2.16 kilograms (“Kg”) as described in ASTM D-1238.

The density of the copolymers typically ranges from about 1.00 to 1.50grams per cubic centimeter (“g/cc”) and preferably from about 1.05 to1.20 g/cc. Preferably, the addition of amorphous blocks or branching(either short and/or long chain) will lower the density of the copolymerrelative to the homopolymer in the solid state. Reducing the density canresult in improved polymer toughness properties. Preferably, thecopolymers of the present invention have a reduction in density of atleast 0.004 g/cc and more preferably from about 0.004 to 0.040 g/ccrelative to a homopolymer of the first monomer (exclusive of initiator.)

Typically, the copolymers of the present invention have a weight averagemolecular weight (Mw) of from about 500 to 800,000 grams/gram mole, andpreferably from about 50,000 to 500,000 grams/gram mole. Typically, thenumber average molecular weight (Mn) ranges from about 500 to 700,000grams/gram mole, preferably from about 30,000 to 500,000 grams/grammole. The Polydispersity Index (M_(w)/M_(n)) typically ranges from about1.3 to 10.

Upon completion of the polymerization reaction, the copolymers can berecovered by any means known to those skilled in the art. Preferably inaccordance with the present invention, the copolymer is transported inits molten state directly to a pelletizer, extruder or molding machinein order to produce the desired product. These products can be producedin any form known to those skilled in art, such as, for example, fibers,pellets, molded articles, films, sheets, and the like.

The films comprising the copolymer compositions of the present inventioncan be converted into cast or blown film, sheet, blow molded, injectionmolded, or spun into fibers using any process or equipment known tothose skilled in the art. Typically, the films have a thickness of fromabout 0.5 to 2 mils, preferably from about 0.6 to 1.7 mils, and morepreferably from about 0.7 to 1.5 mils. The mechanical properties recitedherein are based on a film thickness of 1.0 to 1.3 mils. Typically, thefilms have a MD tensile strength of from about 3000 to 9000 psi,preferably from about 4000 to 8000 psi, with an MD elongation at breakof about 250 to 900 percent, preferably from about 400 to 800 percent,as measured by ASTM D-882. Typically, the films have a TD tensilestrength from about 2000 to 8000 psi, preferably from about 4000 to 6000psi, with an elongation at break of about 300 to 1000 percent,preferably from about 500 to 900 percent. The dart drop impactproperties of the films typically range from about 20 to 200 grams per{fraction (1/1000)} inch (“g/mil”), preferably at least 50 g/mil andmore preferably range from about 50 to 150 g/mil. The MD elmendorf tearproperties of the films typically range from about 5 to 200 g/mil andpreferably range from about 15 to 150 g/mil. The TD elmendorf tearproperties of the films typically range from 100 to 700 g/mil. The MDsecant modulus properties of the films typically range from 30,000 to100,000 psi and preferably range from about 30,000 to 80,000 psi. The TDsecant modulus properties of the films typically range from 30,000 to130,000 psi and preferably range from about 30,000 to 80,000 psi. The MDtensile impact properties of the films typically range from 400 to 1100ft-lb/cu in and preferably range from about 400 to 1700 ft-lb/cu. The TDtensile impact properties of the films typically range from 70 to 1100ft-lb/cu in and preferably range from about 200 to 1700 ft-lb/cu. Thepuncture resistance properties of the films typically range from 3 to 50in-lbs/mil and preferably range from about 10 to 50 in-lbs/mil.

The copolymers of the present invention can be used in the fabricationof a wide variety of products including, for example, sheets, i.e.,greater than 10 mil thick, films, i.e., less than 10 mil thick, e.g.,trash bags, fibers, e.g., sutures, fishing line and non-woven fabricsand molded articles, e.g., containers, tools and medical devices, suchas, for example, staples, clips, pins, prostheses, etc. One particularlypreferred end use in accordance with the present invention is to providecompostable film for use as a trash bag. As defined in ASTM D-883, acompostable plastic is a plastic that undergoes biological degradationduring composting to yield carbon dioxide, water, inorganic compounds,and biomass at a rate consistent with other known compostable materialsand leaves no visually distinguishable or toxic residues.

Typically the copolymers of the present invention are substantiallybiodegradable. More specifically, the copolymer compositions typicallyare biodegradable and compostable by ASTM D-5338, which is a standardtest method for Determining Aerobic Biodegradation of Plastic MaterialsUnder Controlled Composting Conditions.

EXAMPLES

The following Examples are provided for illustrative purposes and arenot intended to limit the scope of the claims which follow.

The following test procedures were used in the Examples.

GPC Test Procedure

GPC was conducted on a Waters 590 HPLC unit having a LC-241 Autosampler,Waters Styragel columns HR-1, HR-3, HR-4, HR-4E, HR-5E, a ERMA ERC-7510Differential Refractometer Detector connected to a VG Data System, usingtetrahydrofuran (stabilized with BHT) as the solvent, 0.45u PTFEdisposable filters (for sample preparation) and a 0.45u Nylon 66 filter(for mobile phase degassing). The unit was calibrated using polystyrenestandards in the molecular weight range of 162 to 1,800,000. Theoperating parameters were:

Flow 1.0 ml/min. Run Time 65 minutes Injection Size 200 μl TemperaturesDetector 35c Columns Ambient Injector Ambient

The sample concentration was 0.5 percent weight/volume.

Melt Flow

Melt flow of the polymers were determined using ASTM D-1238. Thedeterminations were conducted at a temperature of 125° C. and pressureof 2.16 Kg.

Density

The density of polymers were determined using ASTM D-1505, Density ByGradient Column.

Film Properties

Except for puncture resistance, the film properties were measured usingthe appropriate ASTM test procedure, e.g. ASTM D-1709 for Falling DartImpact Resistance (also referred to herein as “dart drop”). Punctureresistance of film was measured using Union Carbide Corporation'sprocedure WC-68-L, and is a test procedure known to those skilled in theart (also referred to herein as “puncture resistance”). Punctureresistance is defined as the force required to rupture a test specimenand the energy absorbed by the film during rupture. Unlike the fallingdart method, which measures high speed impact, the puncture resistanceemploys a slowly moving plunger moving at a crosshead speed of 20inch/minute. An Instron Tensile Tester, compression cell CC (modelG-03-2), integrator, film holder and plunger, calibration weights, andmicrometer are used. Five 6 inch×6 inch samples of each film areprepared and conditioned for 40 hours at 23±2° C. and 50±5% relativehumidity. The thickness of each film is measured in the center to thenearest 0.0001 inch and is mounted on the compression cell so that theplunger will puncture the center of the film. The plunger is positioned8 inch above the compression cell and will have a downward travel of 6inch. The load in pounds required to rupture the samples is recorded andthe results are reported as in-lbs/mil.

Differential Scanning Calorimetry (DSC)

DSC for polymers were measure in a helium atmosphere from −100° C. to85° C. at a rate of 10° C/minute. In place of film properties the effectof crystalline suppression by addition of an amorphous block or shortchain branching was determined using DSC. The effect is shown with adepression of the temperature of crystallization Cc), and on second heatdepression of the melting point (Tm2) and a decrease in crystallinity asmeasured by a reduction in the heat of fusion (ΔH_(f)).

Relaxation Spectrum Index

The RSI of the polymer is determined by first subjecting the polymer toa shear deformation and measuring its response to the deformation usinga rheometer. As is known in the art, based on the response of thepolymer and the mechanics and geometry of the rheometer used, therelaxation modulus G(t) or the dynamic moduli G′(w) and G″(w),wasdetermined as functions of time or frequency.

Biodegradability

ASTM D-5338, which is a standard test method for Determining AerobicBiodegradation of Plastic Materials Under Controlled CompostingConditions, was used to determine the biodegradability of copolymer.

The following ingredients were used in the Examples.

TONES® Monomer ECEQ—a ε-caprolactone monomer available from UnionCarbide Corporation, Danbury, Conn.

TONE Polymer P-787—a polymer of 80,000 Mn available from Union CarbideCorporation, Danbury, Conn.

TONE Polymer P-767—a polymer of 43,000 Mn available from Union CarbideCorporation, Danbury, Conn.

TONE Polymer P-300—a polymer of 10,000 Mn available from Union CarbideCorporation, Danbury, Conn.

Example 1 Preparation of Branched BEPD Adipate Monomers

BEPD adipates in the molecular weight range of 4000 to 21000, asdetermined by GPC, were prepared in a 4-neck resin kettle equipped witha condenser and dean stark trap, agitator, nitrogen sparge tube and flowmeter, and a thermocouple connected to a temperature controlled heatingmantle. On a mole basis, the reactor was charged with the proper amountof BEPD, adipic acid, and 10% toluene by weight as an azeotrope solvent.The azeotrope solvent is included to remove water produced as abyproduct of the reaction. The reaction was conducted under nitrogen andheated to 140° C. After water stopped collecting in the Dean Stark trap,the temperature was raised in 20° C. increments to 220° C. and helduntil >95% of the theoretical amount of water to be removed wasobtained. The temperature was lowered to 160° C., a suitable amount of ametal carboxylate catalyst was charged, the temperature was raised to amaximum of 220° C., and the reaction allowed to continue for 12 to 16hours. The acid number was determined and if >4 additional catalyst wasadded and the reaction cooked until the acid number was <4. The acidnumber and GPC molecular weight of the product were determined.

Example 2 Preparation of Branched BEPD Adipate Caprolactone Copolymers

Caprolactone/BEPD Adipate copolymers were prepared, with GPC molecularweights >40,000, in a 4-neck resin kettle equipped with an agitator,nitrogen sparge tube and flow meter, a thermocouple connected to atemperature controlled oil bath, and vacuum. On a mole basis, thereactor was charged with the proper amount of ε-caprolactone monomer andBEPD Adipate monomer from example 1. Alternately, long chain branchingcan also be included by addition of 20 to 120 ppm trimethylolpropane. Toremove moisture from the reaction the reactants are dried in a nitrogenenvironment at 80° C. under vacuum. After the residual water was reducedto <100 ppm the vacuum was discontinued and the temperature was raisedto 120° C., charged with a suitable amount of a metal carboxylatecatalyst, and then the temperature was increased to obtain a materialtemperature >140° C. The reaction was held at temperature until the %residual ε-caprolactone monomer was <1%. The polymer was discharged andconverted into pellets for extrusion into blown film. The melt index,GPC molecular weight, and RSI values of the polymer were determined.

Example 3 Preparation of Branched Succinate Monomer

Illustrative of incorporating branching using other branching agents, abranched hexanediol ethyl methyl succinate monomer (“HDEMS”) wasprepared by reacting 2-ethyl-2-methylsuccinic acid with 1,6-hexanediol.A procedure substantially similar to that described in Example 1 wasused except that the reaction was discontinued when the acid number wasapproximately 10. A HDEMS having an acid number of 10.1 and GPCmolecular weights of Mn 7628, Mw 22040, Mw/Mn 2.90 was obtained.

Example 4 Preparation of Branched HDEM Succinate Caprolactone Copolymers

A procedure substantially similar to that described in Example 2 wasused to prepare caprolactone/HDEMS copolymers. On a mole basis, thereactor was charged with the proper amount of ε-caprolactone monomer andHDEMS monomer from example 3. Upon completion of the reaction, thepolymer was discharged and converted into pellets for extrusion intoblown film. The melt index and GPC molecular weight were determined.

Example 5 Preparation of BDO Adipate Monomer

A procedure substantially similar to that described in Example 1 wasused to prepare a butanediol (“BDO”) adipate monomer, except that thereaction was discontinued when the acid number was <10. A BDO adipatehaving an acid number of 8.9 and GPC molecular weights of Mn 12000, Mw38395, Mw/Mn 3.20 was obtained.

Example 6 Preparation of Linear BDO Adipate Caprolactone Copolymer

A procedure substantially similar to that described in Example 2 wasused to prepare a caprolactone/butanediol adipate copolymer. On a molebasis, the reactor was charged with the proper amount of ε-caprolactonemonomer and butanediol adipate monomer from example 5. The polymer wasdischarged and converted into pellets for extrusion into blown film. Themelt index and GPC molecular weight were determined.

Control Example 7 Preparation of Butanediol Initiated CaprolactonePolyol

A procedure substantially similar to that described in Example 2 wasused to prepare a butanediol initiated caprolactone polyol. A polyolhaving an acid number of 0.17 and hydroxyl number of 22.10 was obtained.The molecular weight of the polyol based on it's hydroxyl number was5077.

Control Example 8 Preparation of Butanediol Initiated CaprolactonePolyol and Adipoyl-Chloride

The butanediol initiated caprolactone polyol of example 7 was reactedwith adipoyl chloride in a 4-neck resin kettle equipped with a condenserand dean stark trap, agitator, and thermocouple for maintaining controlof a silicone oil bath. The reactor was kept under an inert atmosphereof nitrogen utilizing a dual tube gas manifold connected in parallel toan air-free oil bubbler. Vacuum was applied utilizing the same manifoldconnected in parallel to a Welch high vacuum pump. The polyol wascharged to the reactor and placed under a nitrogen atmosphere. Anhydrous1,2-dichloroethane was introduced into the reactor to facilitate removalof water from the polyol and the temperature was raised to 120° C. Whenthe water was <10 ppm adipoyl chloride, from a clean dry syringe, wasadded to the reactor. The reaction mixture begins foaming, indicatingrapid evolution of hydrogen chloride (“HCL”) gas. After 5 minutes, anitrogen sparge line was introduced into the reactor and the top of thereactor was opened to the atmosphere to facilitate venting of the HCLgas. After an additional 5 minutes, solvent removal was initiated bycontinuously filling and draining distillate from the dean stark trap.The oil bath temperature was slowly raised to 200° C. and maintained for1 hour under a vacuum of <10 mm Hg. After 1 hour, the bath temperaturewas lowered to 160° C. while maintaining vacuum for 15 hours. Theproduct was discharged and it's melt flow was determined.

Example 9 Preparation OF BEPD Initiated Caprolactone Polyol

A procedure substantially similar to that described in Example 2 wasused to prepare a BEPD initiated caprolactone polyol. A polyol having ahydroxyl number of 22 was obtained. The molecular weight of the polyolbased on it's hydroxyl number was 5100.

Example 10 Preparation of BEPD Initiated Caprolactone Polyol andAdipoyl-Chloride

A procedure substantially similar to that described in Example 8 wasused to react the BEPD initiated caprolactone polyol of example 9 withadipoyl chloride. Upon completion the product was discharged and it'smelt flow was determined.

Example 11 Preparation of ε-Caprolactone/t-Butylcaprolactone Copolymer

t-Butylcaprolactone was obtained by conducting the Baeyer Villigerreaction on 4-t-butylcyclohexanone, the details of which are known tothose skilled in the-art. A procedure substantially similar to thatdescribed in Example 2 was used to prepareε-caprolactone/t-butylcaprolactone copolymers. Typically, the reactorwas charged with 95 mole % ε-caprolactone and 5 mole %t-butylcaprolactone. Upon completion the polymers were discharged andtheir melt index and GPC molecular weight were determined.

Example 12 Biodegradability Test

The biodegradability of a BEPD adipate initiated caprolactone copolymerfrom example 2 was determined from the % Theoretical CO₂ produced usingstandard test method ASTM D-5338. A cellulose control was used and thesamples were run in duplicate.

Net Theoretical CO₂ Days Cellulose BEPD ADIPATE Copolymer 1 1.46% 3.16%3 25.37% 13.75% 5 50.03% 21.15% 10 70.04% 43.50% 15 77.15% 75.86% 2084.00% 93.52%

Example 13 Preparation of Compounds and Blown Film Compounding

Blends that were extruded into blown film were compounded on a BrabenderPrep-Center® equipped with four heating zones; a D6/2 42 mm twin screwextruder having counterrotating, intermeshing screws having alength/diameter (L/D) of 7:1; and a pelleting die. Upon exiting theextruder, the compounded strands were passed through a water bathmaintained at 10° C., dried by an air knife, and pelletized. Theoperating parameters were:

Zone Temperature: zones 1 to 4 150°-180° C.

Die Temperature: 150°-180° C.

Melt Temperature: 160°-190° C.

Screw Speed 75 rpm

Blown Film

Both compounded and neat polymers were converted into blown film usingeither the Brabender Prep-Center® or on a Sterling blown film line. TheBrabender Prep-Center® was equipped with a 0.75 inch vented single screwextruder having an L/D of 25:1 and a compression ratio of 2:1, fittedwith a 2 inch blown film die equipped with a 2 inch Brabender single lipair ring with chilled air. The operating parameters were:

Zone Temperature: zones 1 to 4 150°-180° C.

Die Temperature: 150°-180° C.

Melt Temperature: 130°-180° C.

Screw Speed 25 rpm

Gauge: 1-1.5 mils

The Sterling blown film line was equipped with a 1.5 inch single screwlinear low density polyethylene screw having a L:D of 24:1, fitted witha 3 inch die, die gaps of 40 mils or 80 mils, and a 3 inch Sano dual lipair ring with chilled air. The operating parameters were:

Zone Temperature: zones 1 to 4 85°-110° C.

Die Temperature: 95°-110° C.

Melt Temperature: 95°-120° C.

Die Rate 1.40 lb/hr-in

Gauge: 1-1.5 mils

Example 14 RSI Evaluation of Polymers

BEPD adipate polymers prepared according to the procedure set forth inexample 2 were pressed into plaques for evaluation. The polymers of thepresent invention have unique rheological properties that suggest adistinct molecular structure and impart improved toughness in fabricatedblown films. These unique Theological properties also favor relativeease of fabrication into finished articles, especially in filmextrusion. In particular, these polymers have melt indexes (MI) andRelaxation Spectrum Indexes (RSI) such that, for a given polymer areabout 4.0<(RSI)(MI^(0.54)) <about 15.0, or about 4.0 <RSI<30.0, morepreferably about 4.2<(RSI)(MI^(0.54))<about 10.0 or about 4.2<RSI <25.0.

In the formulae immediately above, MI is the melt index of the polymerreported as grams per 10 minutes determined in accordance with ASTMD-1238, condition B, at 125° C. and 2.16kg, and RSI is in dimensionlessunits, measured at 75° C. To compare similar polymers having differentmelt indexes the RSI is normalized according to the above RSI-MIrelationship, where the exponential 0.54 was experimentally determined.

Examples below demonstrate that incorporating just short chain branchingincreases the RSI through broadening of the molecular weightdistribution. Incorporation of both SCB and LCB increase the RSIfurther. TONE® Polymer P-787 is the control and designated as example14-a. This increase in RSI is not only observed in the homopolymersrepresented in examples 14 b-g, but also in example 14-h a compoundedpolymer. Example 14-h is a compounded blend of TONE® Polymer P-300 (alinear 10,000 Mn polymer), a branched PCL copolymer which could not beconverted into film, and the copolymer from example 15-c.

Melt Index, Polymer Example dg/min SCB LCB RSI RSI*MI{circumflex over( )}0.54 Mn a 0.90 N N 5.0 4.8 132700 b 0.98 Y N 6.3 6.2 114510 c 0.93 YY 7.2 6.9 111200 d 2.1 Y N 3.9 5.9 99500 e 2.3 Y Y 5.4 8.5 93300 f 0.36Y N 11.9 6.9 147900 g 0.20 Y Y 21.7 9.6 141000 h 1.88 Y N 6.4 9.0 83570

Example 15 Amorphous Branched Diol Block Effects on Film Properties

BEPD adipate copolymers prepared according to example 2 were convertedinto film on the Brabender using the conditions outlined in example 13.The addition of SCB in the backbone of the adipate prepolymer results inan amorphous adipate block, which leads to improvement in the filmtoughness properties, such as MD Elmendorf tear strength (MDET) and TDtensile impact strength (TDTI). In addition, a more balanced film isachieved as measured by the ratio of MD/TD tensile impact strength. Thetable below shows the improved toughness properties as a result ofincorporation of SCB and LCB. Compared to example 15-a, the TONE®Polymer P-787 control, MD Elmendorf tear strength is improved and inmany cases the TDET is also improved. Once again it was observed thattoughness can be improved by blending as shown in example 15-l, whichhas the same composition as example 14-h.

Polymer MI MDET TDET MDTI TDTI MD/TD Example Mn dg/min SCB LCB g/milg/mil ft-lb/in³ ft-lb/in³ TI a 132700 0.90 N N 11 263 1580 550 2.87 b115600 1.20 Y N 24 350 1410 960 1.47 c 120600 0.59 Y N 16 594 1100 16500.67 d 99500 2.14 Y N 16 179 550 420 1.31 e 107700 1.29 Y N 22 311 980480 2.04 f 111200 0.93 Y Y 25 353 1120 1340 0.84 g 132500 0.46 Y N 18454 980 1280 0.77 h 135300 0.42 Y Y 13 427 900 1350 0.67 I 96600 2.10 YN 41 357 610 580 1.05 j 102500 2.10 Y N 66 307 845 382 2.21 k 92700 2.60Y N 31 234 559 434 1.29 l 83570 1.88 Y N 55 315 885 826 1.07

Example 16 Sterling Film Properties

BEPD adipate colymers prepared in example 2 were converted into film onthe Sterling line, according to the procedure outlined in example 13.Compared to the TONE P787 control, improvements were observed for the TDtensile impact resulting in a more balanced film as measured by theratio of MD/TD tensile impact and tensile strength. The dart drop andpuncture resistance of the copolymer films were significantly improved,the MD tear strength was improved, and the stiffness of the film wasreduced as observed by the lower secant modulus.

Example a b c d PCL Type P-787 BEPD P-787 BEPD Adipate Adipate Melt Flow@125° C./2.16 Kg 0.84 1.72 0.84 1.72 Die Gap (mils) 80 80 40 40 BUR2.2:1 2.2:1 2.1:1 2.2:1 Tensile Strength, MD 9515 7140 7950 6220 (psi)TD 2475 5420 4000 4250 % Elongation MD 600 680 510 625 TD 415 880 590750 Secant Modulus MD 71215 36780 81270 37110 (psi) TD 109200 49060114940 54040 Elemendorf Tear MD 9 25 9 21 (g/mil) TD 293 274 160 283Tensile Impact MD 1060 1300 1017 1120 (ft lb/cu in) TD 318 630 276 625Dart Drop (g/mil) <50 85 <50 74 Puncture Resistance 4 32 4 33(in-lbs/mil)

Example 16 Effect of DIOL Amorphous Block and LCB on Density

The density of polymers produced as described in example 2, wasdetermined. The addition of a BEPD adipate block alone or in combinationwith long chain branching, by the addition of TMP, resulted in lowerdensity copolymers.

POLYMER DENSITY (g/cc) TONE P787 1.136 BEPD ADIPATE COPOLYMER 1.128 BEPDADIPATE/TMP COPOLYMER 1.105

Example 18 HDEMS Brabender Film Properties

HDEMS copolymers prepared according to example 4 were converted intofilm on the Brabender using the conditions outlined in example 13.Compared to the TONE P787, films with significantly improved MD tensileimpact and puncture resistance were obtained.

Puncture MI MDET TDET MDTI TDTI Resistance Example Polymer Type 44 psig/mil g/mil ft-lb/in³ ft-lb/in³ in-lbs/mil a TONE P787 0.91 8 187 700210 3 b HDEMS 1.60 14 265 1270 370 26 c HDEMS 3.00 13 100 1020 115 22

Comparative Example 19 Linear Semi-Crystalline BDO Adipate CopolymerFilm

For comparison to the amorphous branched BEPD adipate copolymers, alinear semi-crystalline caprolactone copolymer was prepared as outlinedin example 6 and converted into film on the Brabender using theconditions outlined in example 13. The semi-crystalline block providedby the butanediol adipate monomer, resulted in a polymer having lowertear strength, tensile impact, and puncture resistance compared topolymers from example 2.

Puncture MDET TDET MDTI TDTI Resistance Example Polymer Type MI 44 psig/mil g/mil ft-lb/in³ ft-1b/in³ in-lbs/mil a BEPD 2.00 55 285 790 415 33ADIPATE b BEPD 1.60 32 320 1018 622 35 ADIPATE c BDOA 2.30 19 174 179 993

Example 20 Influence of Blocks on Copolymer Melting Point andCrystallinity

Caprolactone polyols were initiated with BDO (example 7) or BEPD(example 9) and chain extended with adipoyl chloride as discussed inexamples 8 and 10, respectively. DSC shows that compared to the TONEP787 control, the melting point, crystallization temperature (Tc), andcrystallinity are significantly reduced by inclusion of the amorphousBEPD block. The semi-crystalline BDO block results in an increase in Tc.It was found that the semi-crystalline BDO block provided poor filmproperties.

TYPE Tm2 (° C.) ΔH_(f) cal/g Tc (° C.) P787 53.34 15.12 17.44 BDO 50.3514.01 19.93 BEPD 47.07 7.52 11.00

Example 21 Influence of Branched Caprolactone on Melting Point andCrystallinity

A ε-caprolactone/t-butylcaprolactone copolymer, prepared as discussed inexample 11 was compared to TONE P767 by DSC. Inclusion of the branchedcaprolactone monomer resulted in a reduction of the melting temperature,crystallinity, and crystallization temperature.

TYPE Tm2 (° C.) ΔH_(f) cal/g Tc (° C.) P767 53.06 16.95 18.16 t-butylcap 49.58 15.77 11.45

In addition to the specific aspects of the invention disclosed herein,those skilled in the art will recognize that other aspects are intendedto be within the scope of the invention.

We claim:
 1. A copolymer polymerized from: (a) a first monomer which ispolymerizable by condensation polymerization; and (b) a second monomerwhich is copolymerizable with the first monomer: wherein the secondmonomer is: (i) effective to suppress the crystallinity of thecopolymer: (ii) an initiator for the polymerization of the first monomerprovided that the second monomer does not comprise the first monomer;and (iii) present in an amount of from about 5 to 35 weight percentbased on the monomers used to make the copolymer.
 2. The copolymer ofclaim 1 which is biodegradable.
 3. The copolymer of claim 1 wherein thefirst monomer has a functional group selected from the group consistingof esters, ethers, carbonates, acetals, alcohols, acids, amines, amides,acid halides, isocyanates and mixtures thereof.
 4. The copolymer ofclaim 1 wherein the first monomer is cyclic.
 5. The copolymer of claim 1wherein the first monomer is selected from the group consisting oflactones, lactides, lactams, polyols, urethanes, ureas, carbonates,acetals, and mixtures thereof.
 6. The copolymer of claim 1 wherein thefirst monomer is selected from the group consisting of caprolactone andderivatives thereof.
 7. The copolymer of claim 1 wherein the secondmonomer has a functional group selected from the group consisting ofesters, ethers, carbonates, acetals, alcohols, acids, amines, amides,acid halides, isocyanates and mixtures thereof.
 8. The copolymer ofclaim 1 wherein the second monomer is selected from the group consistingof adipate esters and lactones.
 9. The copolymer of claim 1 wherein thesecond monomer is effective to introduce amorphous regions in thecopolymer.
 10. The copolymer of claim 1 wherein the second monomer iseffective to introduce branching into the copolymer.
 11. The copolymerof claim 1 wherein the second monomer is a prepolymer having a numberaverage molecular weight of from about 500 to 25,000 g/gmole.
 12. Thecopolymer of claim 1 which is polymerized from about 99 to 80 weightpercent of the first monomer and from about 1 to 20 weight percent ofthe second monomer.
 13. The copolymer of claim 1 wherein the copolymerhas a crystallization temperature depression of at least about 2° C. 14.The copolymer of claim 1 which has a reduction in density of at leastabout 0.004 g/cc.
 15. A film made from the copolymer of claim
 1. 16. Thefilm of claim 15 having a puncture resistance of from about 3 to 50in-lbs/mil.
 17. The film of claim 15 having a dart drop of at least 50g/mil.
 18. A method of enhancing the toughness of a film, said methodcomprising using the polymer of claim 1 to make said film.
 19. A processfor making a copolymer, comprising polymerizing a first monomer which ispolymerizable by condensation polymerization with a second monomer whichis copolymerizable with the first monomer: characterized in that thesecond monomer is: (i) effective to suppress the crystallinity of thecopolymer; (ii) an initiator for the polymerization of the first monomerprovided that the second monomer does not comprise the first monomer;and (iii) present in an amount of from about 5 to 35 weight percentbased on the monomers used to make the copolymer.
 20. A molded articlemade from the copolymer of claim
 1. 21. The film of claim 15 having avalue of RSI.MI 0.54 of at least 1.0 units greater than a film made froma homopolymer of the first monomer.